1. Field of the Invention
The invention relates to an electric power system having a generator driven by an engine and power conditioners, and enabled to supply individual electric power generated by the generator and external electric power to load by connecting an output wire of the generator with an external electric power system such as a commercial electric power system through the power conditioners. Especially, it relates to operation control construction of the power conditioners, connection construction of inverter circuits of the power conditioners, and connection construction of multiple electric power systems.
2. Related Art
In recent, a gas cogeneration system attracts public attention as a kind of independent power generation systems. It is a system which provides electric power generated from fuel of natural gas, and recovers waste heat for heating water or the like.
The system comprises: a generator for converting fuel energy into electric energy; a electric power conversion device (an inverter circuit) for converting electric power from the generator into alternating-current power synchronized with an external electric power source such as a commercial electric power source; a protection device for detecting the abnormalities of the external electric power source; and a waste heat recovery device for recovering waste heat. A power conditioner is constituted by the electric power conversion device and the protection device.
When the electric power generated by the gas cogeneration system causes reverse power flow, the efficiency of power generation falls. Therefore, functions for detecting and preventing the reverse power flow are needed.
For increasing the capacity of an electric power system such as the gas cogeneration system, enlarging capacity of the inverter circuit poses a problem in respect of retaining the system compact. Then, it may be considered that multiple power conditioners (namely, multiple inverter circuits) are connected to the external electric power system.
However, when connecting multiple power conditioners (multiple inverter circuits) to the external electric power such as a commercial electric power system, all the power conditioners are required to detect the reverse power flow. Also, it is important to prevent inequality of output among the power conditioners, and to ensure a compact interconnection structure among the inverter circuits of the power conditioners simply and inexpensively.
Furthermore, when a plurality of the electric power systems are provided, it is necessary to equalize operation of the systems.